Plant hormones play important roles in plant growth responses. Ethylene is a plant growth hormone, which affects many important aspects of plant growth, development, and senescence. The most important effects of ethylene include processes associated with the ripening of fruits, the senescence of flowers, and the abscission of leaves. The commercial value of fresh produce is usually reduced by the excessive amount of ethylene gas which hastens the ripening of fruits, the senescence of flowers, and the early abscission of leaves.
Because of ethylene-induced problems, intensive research has been focused on ways to prevent or reduced its effects on plants. One of the most effective ways of mitigating the effects of ethylene employs the principle of blocking the receptor in plants that receives signals from ethylene. One of the best-known compounds for such a purpose is silver thiosulfate (“STS”). STS provides an irreversible blocking of the ethylene binding sites in plant cells and thereby prevents or reduces the harmful effects of ethylene on plants. While STS is highly effective, it poses a serious waste disposal problem since silver is a heavy metal that is toxic to most living organisms.
Sisler et al., Plant Growth Reg. 9, 1587-164, 1990 discloses that cyclopentadiene is an effective blocking agent for an ethylene binding site. An effective diazocyclopentadiene is also disclosed in U.S. Pat. No. 5,100,462. However, the cyclopentadiene and diazocyclopentadiene are unstable and have a strong odor.
U.S. Pat. No. 5,518,988 discloses the use of gaseous cyclopropene and derivatives thereof such as methylcyclopropene, as ethylene binding site blocking agents. Methylcyclopropene is effective at a very low dosage, in the parts per billion range, and is safe to be used in fruits and vegetables, as well as flowers. Methylcyclopropene is readily undergoing oxidation and other reactions so that it is highly unstable. Most recently, U.S. Pat. No. 6,017,849 encapsulates methylcyclopropene gas by a carrier. The carrier such as alpha-cyclodextrin serves to stabilize the reactivity and instability of cyclopropene gas, thereby providing a convenient and safe means of storing, transporting and applying or delivering the gas to plants.
Commercial methylcyclopropene powder products usually contain 0.43% of a methylcyclopropene gas ingredient. The gas will be released after mixing the powder with water or a buffer solution. An application rate of 0.5 g of powder per one cubic meter of the sealed space results in a final methylcyclopropene concentration of 900 parts per billion. The shelf life of flowers, fruits and vegetables can be significantly ended if they are exposed at this concentration for at least 4 hours as a post-harvest treatment.
The powder products are much more convenient to use than the products in a gas form, but are by no means user-friendly. It still has the disadvantages related to powder handling in the field, e.g. susceptibility to premature wetting and errors in measurement. Furthermore, manual mixing is normally recommended when a large quantity of powder, such as amounts more than 10 g per batch, is required for fumigating a large space. The amount of methylcyclopropene in the enclosed space may be reduced from its originally intended level due to personal entering and leaving of the enclosed space during the mixing procedure, and thus the beneficial effect of methylcyclopropene is reduced.
The present invention provides an effervescent tablet formulation which alleviates the disadvantages of mixing associated with the powder form.